Certain water soluble sulfonated phthalocyanines are efficient photosensitizers for killing mammalian cells are appear to be promising candidates for replacing hematoporphyrin derivative in photodynamic therapy (PDT) of human tumors. The post- illumination photohemolysis of human red blood cells was used as a model system for studying membrane damage sensitized by various sulfonated phthalocyanines. Scavenger studies with tryptophan (which reacts rapidly with singlet oxygen) and mannitol (which reacts rapidly with hydroxyl radicals but not with singlet oxygen) are consistent with the predominant role of singlet oxygen in the photohemolysis sensitized by sulfonated aluminum phthalocyanine. Similar results have been obtained in preliminary experiments for the photosensitized cell killing of V- 79 Chinese hamster cells. The chemical effect of ultrasound are being investigated in relation to hyperthermia (used in combination with radiation therapy) and the possible effects of diagnostic and therapeutic applications. In the process of transient cavitation, the collapsing cavitation bubbles result in very high temperatures (greater than 5000 degrees C) and pressures which lead to the dissociation of water to hydrogen atoms and hydroxyl radicals. For solutions containing volatile compounds such as alcohols, the reaction products are those typical of combustion processes (in the collapsing bubbles) and those similar to the effects of ionizing radiation due to the hydrogen atoms and hydroxyl radicals which escape into the bulk of the solution to react with solute molecules. In the case of methanol, methyl radicals formed by the high temperature dissociation of the carbon-oxygen bond, as well as radicals formed by the reactions of hydrogen atoms and hydroxyl radicals with methanol were detected by spin trapping and electron spin resonance. The radicals produced in the sonochemistry of nucleic acid bases, nucleosides, amino acids and peptides have been identified by spin trapping.